This invention relates to dinitromethane and to a process for synthesizing its alkali metal salts. More particularly, this invention concerns itself with an economical and practical route for synthesizing the alkali salts of dinitromethane which involves the use of methyl cyanooximinoacetate and methyl cyanodinitroacetate as reaction components.
The salts of dinitromethane find wide use as intermediate and starting materials in the preparation of polynitro explosives and advanced energetic propellants. They also find application as reaction components in the preparation of a wide variety of geminal dintro-compounds. The variety of applications for which these materials find use amply demonstrates their importance to the chemical industry. Unfortunately, the methods utilized in the past for effecting the synthesis of the alkali metal salts of this invention, did not provide an efficient and economical means for their production in reasonably large quantities. The necessity for providing a practical route which could lead to reduced cost production, therefore, become obvious.
Free dinitromethane is an unstable pale yellow oil that decomposes vigorously even at ambient temperatures. The alkali salts of dinitromethane, however, are stable compounds having a wide utility as key intermediates in chemical syntheses.
The potassium salt of dinitromethane was first prepared by the reduction of potassium bromonitromethane with hydrogen sulfide in accordance with the method of F. Villiers, Bull. Soc. Dhim. Fr., 41, 251 (1884). More recently, potassium dinitromethane has been prepared by the Ter Meer reaction of chloronitromethane as shown in H. Ferer et al, J. An. Chem. Soc., 73 1360 (1951). Unfortunately, this reaction only produces yields of about 23 percent. The dinitromethane salts can also be obtained from the alkali salts of dinitroethanal according to the methods shown by P. Noble et al, Chem, Rev., 64 19 (1964).
The alkali salts of dinitromethane have proven to be very useful as starting materials in the synthesis of geminal dinitro compounds. For example, potassium dinitromethane reacts readily with one or two mole of formaldehyde to give potassium dinitroethanal and 2,2-dinitropropanedial, respectively. The fluorination of alkali salts of dinitroethanol, in turn, produces fluordinitroethanol. Fluorodinitromethane and 4,4-dinitropimelic acid are other geminal dinitro intermediates found to be useful in the synthesis of polynitro explosives and propellants.
From the above examples, it can be seen that dinitromethane salts are important and find wide application as key intermediates in a variety of chemical syntheses. Consequently, a considerable research effort has evolved in an attempt to find efficient economical and practical routes for preparing the alkali salts of dinitromethane.
Heretofore, the lack of a practical route necessitated the use of methods based on the Ter Meer method, the use of nitroform, or the oxidative nitration reaction.
Nitroform, used in the synthesis of fluorodinitroethanol, is produced by nitration of acetylene or acetone. Both processes produce large amounts of nitrogen oxides which present expensive pollution problems. In its applications, for the synthesis of gemminal dinitro compounds, one nitro group of nitroform must be removed adding to the cost of this process.
In the oxidative nitration route, gem-dinitro compounds are prepared by reacting mononitro compounds with a mixture of silver nitrate and sodium nitrite. In a large scale production this method requires a large capital investment in silver nitrate and also suffers from mechanical losses of silver.
The Ter Meer reaction is limited to the synthesis of terminal geminal dinitro compounds. As already indicated, the yield of dinitromethane in the Ter Meer method is low. Also, in many cases, nitrohalo starting materials needed in this reaction cannot be obtained in good yields. With the present invention, however, the problems associated with these prior art methods have been overcome by the process of this invention in which the synthesis of the alkali metal salts of dinitromethane has been accomplished by effecting the nitration of methyl cyanooximinoacetate to form methyl cyanodinitroacetate which in turn is reacted with an alkali metal hydroxide, such as potassium or sodium hydroxide, to effect its saponification and resulting production of the respective alkali metal salt of dinitromethane. This unique method provides a solution to the problem of finding a practical and economical route for synthesizing these useful intermediate reactants, in relatively high yield.